The invention relates to methods and compositions useful for rehabilitating underground pipe in place. In a further aspect, the invention relates to epoxy resin pipe liners containing curing agents which impart controlled, hard cure in moist environments and have long working lives.
Repairing underground pipelines, such as water, chemical and sewer pipes, can be an expensive and difficult task. Such underground pipelines are subject to fracture and corrosion, resulting in uneven flow within the pipe, leakage of fluid and, eventually, complete rupture of the pipe. Repair of the ruptured or leaking pipe can involve time-consuming and expensive excavation and replacement of the damaged pipe and, in the case of pipelines extending under roads and buildings, for example, can be extremely costly or impractical.
Various means have been devised to repair lengths of underground pipe in place, without excavation and removal of the pipe. One such method involves lining the interior of a pipe with a nonwoven felt impregnated with a catalyzed liquid thermosetting resin. The felt is inverted into one end of the pipe to be repaired in such a way that the resin-impregnated felt is positioned against the interior walls of the pipe, and the thermosetting resin is then cured, in situ, to form a cured functional resinous pipe within and adhering to the treated pipe. Such a method repairs defects in the pipe and protects the pipe from further deterioration. There are numerous difficulties in carrying out such a process, which makes stringent demands on the resin/curing agent system used. The system must have low shrinkage of the thermosettable material during and after cure, which could result in cracking of the cured material. Moisture is almost invariably present during the cure, and slow or incomplete cure results from attempting in situ cure of a moisture-sensitive system. If the thermosettable system is subject to rapid, uncontrollable exotherm during cure, excessive heat can be generated and degradation of the lining material can result. If the pipe lining job involves the repair of pipe corroded completely through, it is necessary to use a resin system which exhibits good creep resistance, or the liner will fail. The working life of the resin/curing agent system, by which is meant the time after mixing the curing agent with the resin during which the system is sufficiently flexible to permit application to the felt and insertion of the felt into the pipe, must be long enough to permit convenient application in the field at ambient temperatures, which can vary widely with location, and yet be sufficiently reactive to harden in a reasonable time at temperatures obtainable from a boiler truck in a field operation.
Polyester is used as a pipe-liner resinous material, but because of its high shrinkage and styrene boil, it is used only for ambient temperature and pressure applications. "Styrene boil" is the generation of styrene vapor in the polyester matrix from excessive heat build-up during cure. Styrene boil results in a porous pipe lining, which is unsuitable for high-pressure pipelines. Because of the need for relatively rapid cure of pipe-lining systems and the difficult conditions under which cure of in situ pipe liners is carried out, resistance to uncontrollable exotherming and the evolution of vapors is an important property of pipe-lining system. Polyester liners are also very susceptible to shrinkage, commonly exhibiting a volume shrinkage of 6-10%. Epoxy resins cured with 1-substituted imidazoles, such as the reaction product of imidazole and propylene oxide, have also been used. Such systems have been found to be sensitive to moisture and exotherm in the curing environment. Because the environment of in situ pipe-lining invariably includes water and heat, moisture and exotherm insensitivity are very important properties of pipe-lining systems. Such systems are somewhat susceptible to shrinkage, exhibiting a volume shrinkage of 2-3%.
For in situ pipe repair, it is therefore necessary to design thermosetting resin systems which have a combination of properties including moisture and shrink resistance, creep resistance, controllable exotherm, good cured flexibility and strength, short cure time at moderate temperatures, and long system working life.
It is therefore an object of the present invention to provide an improved process for in situ formation using a thermosettable epoxy resin system.